The invention relates to a centrifuge having a system for controlling the temperature of the liquid to be centrifuged or of one of the components thereof, consisting of an insert which is inserted into the drum and whose outer periphery forms at least one passage which is provided with an inlet and a discharge for the temperature control medium and is separated from the separating chamber of the drum.
Such a centrifuge is known, for example, from German Pat. No. 437,482. The temperature control system is intended for the purpose of delivering heat to the solids of low melting point which are separated from the liquid being centrifuged and collect in the peripheral part of the drum, in order to make them fluid and continuously removable.
In the pharmaceutical industry it is necessary in many cases to keep the temperature of the liquid as constant as possible during the centrifuging operation, after the temperature has been established at a certain level. This is the case, for example, with human blood, when certain proteins are to be precipitated from the plasma thereof at different temperatures and removed by centrifugation for use in combatting certain diseases. The blood which is collected, and must be kept at a low temperature, is adjusted to the temperature required for the removal of a specific protein, and it must be maintained at that level within no more than fractions of a degree during the centrifugation if the protein in question is to be obtained in pure form. Since the winning of the individual fractions takes place at relatively low temperatures, the blood must be prevented from heating during centrifugation.
It is known that the friction between a rotating body and the air surrounding it depends to a great extent on its diameter. A drum of average size can be warmed by such friction to temperatures of as much as about 80.degree.C. Due to the high heat transfer coefficient of the drum material, the friction heat which thus develops is transfered to the liquid being centrifuged, and the lower the throughput is, the higher the temperature of the liquid will become. But since blood centrifuges have to be operated at a low throughput, special precautions must be taken to prevent warming of the blood during centrifugation. Without such measures the fractionation of human blood by centrifugation is simply impossible.
Although the apparatus known from German Pat. No. 437,482 is fundamentally capable of being charged with a cooling liquid, it is unsuited for coolants having a low vaporization point. The warming of the drum periphery itself is not counteracted, so that the coolant exceeding the vaporization point would pass out in vapor form into the catcher and would not be able to be recovered, not to mention the fact that the vapors may result in a hazardous contamination of the air in the work room. This known temperature control system furthermore has the disadvantage that the insert would collapse under the pressure of the drum charge due to the lack of support of its inner wall, if the channels were to empty themselves. To prevent such collapse the inlet outlet are drawn far inwardly so that the passages will remain filled after the temperature control medium is shut off. This simultaneously prevents the temperature control medium from mixing with the liquid being centrifuged.
On the other hand, experiments have shown that the warming of the drum periphery virtually cannot be prevented by a cooling jacket disposed in the frame surrounding the drum. The heat transfer coefficient of the air between the drum and the frame is so low that an extraordinarily low temperature would have to be produced with the cooling jacket in order to permit the heat that is produced to be carried away from the periphery of the drum.